package handlers

import (
	"errors"
	"fmt"
	"io/fs"
	"path/filepath"
	"time"

	"github.com/dustin/go-humanize"
	"gorm.io/gorm"
	"sneak.berlin/go/webhooker/internal/database"
	"sneak.berlin/go/webhooker/internal/delivery"
)

// TargetRowView is one row of the target list on a webhook's page.
type TargetRowView struct {
	delivery.TargetView

	// Deliveries counts the target's delivered and failed deliveries,
	// and is nil when the webhook's event database could not be read.
	Deliveries *TargetDeliveries

	// Archive is a database target's archive file, and nil for a target
	// of any other type.
	Archive *ArchiveFileView

	// Paused is set while the target's circuit breaker is turning its
	// deliveries away, and nil otherwise.
	Paused *PausedView
}

// PausedView is a target's circuit breaker turning deliveries away.
// While the breaker is open, Until is a time in UTC, and Relative how
// long that is from now: on the target's row, when the cooldown ends;
// on a delivery, the earliest it can be tried next. While it is
// half-open both are empty: the cooldown has ended, and the target's
// deliveries are held while one delivery tests whether the target has
// recovered.
type PausedView struct {
	Until    string
	Relative string
}

// pausedView reads the target's circuit breaker for its row, and
// returns nil when the breaker lets the target's deliveries through.
func (h *Handlers) pausedView(targetID string) *PausedView {
	state, cooldown := h.breakers.StateAndCooldown(targetID)

	switch {
	case state == delivery.CircuitHalfOpen:
		return &PausedView{}
	case state == delivery.CircuitOpen && cooldown > 0:
		return newPausedView(time.Now().Add(cooldown))
	default:
		return nil
	}
}

// deliveryPausedView reads the circuit breaker of a retrying delivery's
// target. While it is open, it says the earliest the delivery can be
// tried next: the later of the cooldown's end and the end of the
// delivery's own backoff after its last attempt. It is only the
// earliest: when the cooldown ends, one of the target's waiting
// deliveries is sent to test it while the others wait at least one more
// cooldown. Otherwise it returns nil, half-open included, since the
// delivery may then be the one being sent to test the target.
func (h *Handlers) deliveryPausedView(
	targetID string, attempts []deliveryResultRow,
) *PausedView {
	state, cooldown := h.breakers.StateAndCooldown(targetID)
	if state != delivery.CircuitOpen || cooldown <= 0 {
		return nil
	}

	next := time.Now().Add(cooldown)

	if len(attempts) > 0 {
		last := attempts[len(attempts)-1]

		backoffEnd := last.CreatedAt.Add(delivery.Backoff(last.AttemptNum))
		if backoffEnd.After(next) {
			next = backoffEnd
		}
	}

	return newPausedView(next)
}

// newPausedView is a PausedView of deliveries paused until the given
// time. A time not on the current UTC day is written with its date, as
// the event log writes its times.
func newPausedView(until time.Time) *PausedView {
	until = until.UTC()

	layout := time.TimeOnly
	if until.Format(time.DateOnly) != time.Now().UTC().Format(time.DateOnly) {
		layout = time.DateTime
	}

	return &PausedView{
		Until:    until.Format(layout) + " UTC",
		Relative: humanize.Time(until),
	}
}

// TargetDeliveries is how many of a target's deliveries became
// delivered and how many failed: in total, which retention does not
// reduce, and in the last 24 hours. Deliveries still pending or
// retrying count in neither.
type TargetDeliveries struct {
	Delivered int64
	Failed    int64

	DeliveredLast24Hours int64
	FailedLast24Hours    int64
}

// ArchiveFileView is what a database target's row shows about its
// archive file.
type ArchiveFileView struct {
	Name string

	// Note stands in for the size and the last write when there are
	// none to show, and is empty when there are.
	Note string

	// Size is the size on disk. Written is how long ago the file was
	// last written, and WrittenUTC the full time the page shows on
	// hover.
	Size       string
	Written    string
	WrittenUTC string
}

// targetRows projects a webhook's targets for the target list on its
// page.
func (h *Handlers) targetRows(
	webhook *database.Webhook, targets []database.Target,
) []TargetRowView {
	views := delivery.NewTargetViews(targets)
	rows := make([]TargetRowView, len(views))

	deliveries, err := h.loadTargetDeliveries(webhook.ID)
	if err != nil {
		h.log.Error(
			"failed to read target delivery counts",
			"webhook_id", webhook.ID,
			"error", err,
		)
	}

	// NewTargetViews returns one view per target, in order.
	for i := range views {
		rows[i].TargetView = views[i]

		if err == nil {
			counts := deliveries[targets[i].ID]
			rows[i].Deliveries = &counts
		}

		if targets[i].Type == database.TargetTypeDatabase {
			rows[i].Archive = h.archiveFileView(webhook, &targets[i])
		}

		rows[i].Paused = h.pausedView(targets[i].ID)
	}

	return rows
}

// loadTargetDeliveries reads the delivery counts of a webhook's targets
// from its event database, keyed by target. A target with no deliveries
// is left out, and so is every target when the event database does not
// exist yet, since opening it would create it.
func (h *Handlers) loadTargetDeliveries(
	webhookID string,
) (map[string]TargetDeliveries, error) {
	if !h.dbMgr.DBExists(webhookID) {
		return map[string]TargetDeliveries{}, nil
	}

	webhookDB, err := h.dbMgr.GetDB(webhookID)
	if err != nil {
		return nil, err
	}

	return readTargetDeliveries(webhookDB, time.Now())
}

// readTargetDeliveries counts each target's deliveries that became
// delivered and those that failed: in total from the targets' running
// totals, and in the 24 hours before now from the deliveries' status
// index. Each is one query for all the targets, and neither reads every
// stored delivery.
func readTargetDeliveries(
	db *gorm.DB, now time.Time,
) (map[string]TargetDeliveries, error) {
	var totals []database.TargetTotals

	err := db.Find(&totals).Error
	if err != nil {
		return nil, fmt.Errorf("reading target totals: %w", err)
	}

	lastDay, err := finishedByTarget(db, now.Add(-longWindow))
	if err != nil {
		return nil, err
	}

	byTarget := make(map[string]TargetDeliveries, len(totals))

	for _, total := range totals {
		byTarget[total.TargetID] = TargetDeliveries{
			Delivered: total.Delivered,
			Failed:    total.Failed,
		}
	}

	for _, finished := range lastDay {
		counts := byTarget[finished.TargetID]
		counts.DeliveredLast24Hours = finished.Delivered
		counts.FailedLast24Hours = finished.Failed
		byTarget[finished.TargetID] = counts
	}

	return byTarget, nil
}

// archiveFileView describes a database target's archive file from the
// file's metadata alone; the archive is never opened. The file is found
// by the name the archive writer uses, so it follows a rename of the
// webhook or the target.
func (h *Handlers) archiveFileView(
	webhook *database.Webhook, target *database.Target,
) *ArchiveFileView {
	path := delivery.ArchivePath(h.dbMgr, webhook, target)
	view := &ArchiveFileView{Name: filepath.Base(path)}

	file, err := delivery.StatArchive(path)

	switch {
	case errors.Is(err, fs.ErrNotExist):
		view.Note = "not created yet"
	case err != nil:
		h.log.Error(
			"failed to read archive file metadata",
			"target_id", target.ID,
			"error", err,
		)

		view.Note = "could not be read"
	default:
		view.Size = humanize.Bytes(uint64(file.Size)) //nolint:gosec // never negative
		view.Written = humanize.Time(file.Written)
		view.WrittenUTC = file.Written.UTC().Format(time.DateTime) + " UTC"
	}

	return view
}